JP7293004B2 - Optical scanning device and image forming device - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to an optical scanning device and an image forming apparatus.

An electrophotographic image forming apparatus forms an electrostatic latent image on an image plane by scanning a beam. At this time, the image forming apparatus reshapes the cross-sectional shape of the beam with an aperture for the purpose of improving image quality. The beam shaped by the diaphragm is reflected by a rotating polygon mirror and scanned across the image plane through a scanning optical system.

JP-A-10-104540

If the image forming apparatus can use a plurality of types of polygon mirrors with different numbers of faces, it is possible to use a common housing and the like, and thus it is possible to reduce costs. However, if the number of faces of the polygon mirror is increased, vignetting will occur in the beam.

A problem to be solved by the embodiments of the present invention is to provide an optical scanning device and an image forming device that can use a plurality of types of polygon mirrors with different numbers of faces.

An optical scanning device according to an embodiment includes a first light source, a second light source, a first aperture section, a second aperture section, and a deflector. The first light source emits a first light flux. The second light source emits a second light beam having an opening angle with respect to the first light beam in the main scanning direction, and is located upstream of the first light source in the main scanning direction. The first aperture unit adjusts the shape of the first light beam to a first length from the optical axis to the upstream end in the main scanning direction, and a first length from the optical axis to the downstream end in the main scanning direction. Trim the length to a second length that is greater than the first length. The second aperture unit adjusts the shape of the second light flux to the third length from the optical axis to the upstream end in the main scanning direction, and the third length from the optical axis to the downstream end in the main scanning direction. Trim the length to a fourth length that is less than the third length. The deflector deflects the first light flux and the second light flux that have passed through the first aperture section and the second aperture section at positions shifted in the sub-scanning direction on the same plane.

1 is a diagram showing an example of a schematic configuration of an image forming apparatus according to an embodiment; FIG. FIG. 2 is a diagram showing an example of a schematic configuration of an image forming unit in FIG. 1; FIG. 2 is a block diagram showing an example of the circuit configuration of the main part of the image forming apparatus shown in FIG. 1; FIG. 2 is a diagram showing an example of an optical scanning device in FIG. 1; FIG. 2 is a plan view of an example of the optical system of the optical scanning device in FIG. 1 ; FIG. 6 is a partial enlarged view partially enlarging the main part of FIG. 5; The figure which looked at the structure of FIG. 6 from the side. FIG. 6 is a diagram showing an example of a main scanning diaphragm in FIG. 5; FIG. 6 is a diagram showing an example of a main scanning diaphragm in FIG. 5; FIG. 5 is a diagram showing a comparative example of a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 4 is a diagram for explaining a main scanning diaphragm; FIG. 5 is a diagram showing a modification of the main scanning diaphragm; FIG. 6 is a diagram showing an example of a main scanning diaphragm in FIG. 5; FIG. 6 is a diagram showing an example of a main scanning diaphragm in FIG. 5; FIG. 5 is a diagram showing a modification of the main scanning diaphragm;

An image forming apparatus according to an embodiment will be described below with reference to the drawings. It should be noted that the scale of each part of each drawing used for the description of the following embodiments may be changed as appropriate. Also, in each drawing used for the description of the embodiments below, the configuration may be omitted for the sake of description.

FIG. 1 is a diagram showing an example of a schematic configuration of an image forming apparatus 100 according to an embodiment.
The image forming apparatus 100 is, for example, an MFP (multifunction peripheral), a copier, a printer, a facsimile machine, or the like. However, the following description assumes that the image forming apparatus 100 is an MFP. The image forming apparatus 100 has, for example, a printing function, a scanning function, a copying function, an erasing function, a facsimile function, and the like. The printing function is a function of forming an image on the image forming medium P or the like using a recording material such as toner. The image forming medium P is, for example, a sheet of paper. The scanning function is a function of reading an image from a document on which an image is formed. The copy function is a function of printing an image read from a document or the like using the scan function on the image forming medium P using the print function. The erasing function is a function of erasing an image formed on the image forming medium P with an erasable recording material. The image forming apparatus 100 includes a printer 101, a scanner 102, and an operation panel 103, for example.

A printer 101 is a device having a printing function. The printer 101 includes, for example, a paper feed tray 111, a manual feed tray 112, a paper feed roller 113, a toner cartridge 114, an image forming unit 115, an optical scanning device 116, a transfer belt 117, a secondary transfer roller 118, a fixing unit 119, a duplex It includes a unit 120 and an output tray 121 .

The paper feed tray 111 accommodates image forming media P used for printing.
The manual feed tray 112 is a table for manually feeding the image forming medium P. As shown in FIG.
The paper feed roller 113 is rotated by a motor to carry out the image forming medium P accommodated in the paper feed tray 111 or the manual feed tray 112 from the paper feed tray 111 or the manual feed tray 112 .

The toner cartridge 114 stores recording materials such as toner to be supplied to the image forming unit 115 . Image forming apparatus 100 includes a plurality of toner cartridges 114 . As an example, as shown in FIG. 1, image forming apparatus 100 includes four toner cartridges 114: toner cartridge 114C, toner cartridge 114M, toner cartridge 114Y, and toner cartridge 114K. The toner cartridge 114C, the toner cartridge 114M, the toner cartridge 114Y, and the toner cartridge 114K each store recording material corresponding to each color of CMYK (cyan, magenta, yellow, and key). That is, the toner cartridge 114C stores cyan (C) recording material. The toner cartridge 114M stores a magenta (M) recording material. The toner cartridge 114Y stores a yellow (Y) recording material. The toner cartridge 114K stores black (K) recording material. Note that the colors of the recording material stored in the toner cartridge 114 are not limited to the colors CMYK, and may be other colors. Also, the recording material stored in the toner cartridge 114 may be a special recording material. For example, the toner cartridge 114 stores an erasable recording material that becomes invisible at a temperature higher than a predetermined temperature.

Image forming apparatus 100 includes a plurality of image forming units 115 . As an example, as shown in FIG. 1, the image forming apparatus 100 includes four image forming units 115: an image forming unit 115C, an image forming unit 115M, an image forming unit 115Y, and an image forming unit 115K. The image forming unit 115C, the image forming unit 115M, the image forming unit 115Y, and the image forming unit 115K form images using recording materials corresponding to the respective colors of CMYK. That is, the image forming unit 115C forms a cyan image. Image forming unit 115M forms a magenta image. Image forming unit 115Y forms a yellow image. The image forming section 115K forms a black image.

Image forming unit 115 will be further described with reference to FIG. FIG. 2 is a schematic diagram showing an example of a schematic configuration of the image forming unit 115. As shown in FIG. The image forming section 115 includes, for example, a photosensitive drum 1151 , a charging unit 1152 , a developing unit 1153 , a primary transfer roller 1154 , a cleaner 1155 and a static elimination lamp 1156 .

A beam B emitted from the optical scanning device 116 hits the photosensitive drum 1151 . Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 1151 .
The charging unit 1152 charges the surface of the photosensitive drum 1151 with a predetermined positive charge.

The developing unit 1153 develops the electrostatic latent image on the surface of the photosensitive drum 1151 using the recording material D supplied from the toner cartridge 114 . As a result, an image of the recording material D is formed on the surface of the photosensitive drum 1151 .

The primary transfer roller 1154 is arranged at a position facing the photosensitive drum 1151 with the transfer belt 117 interposed therebetween. A primary transfer roller 1154 generates a transfer voltage with the photosensitive drum 1151 . Thereby, the primary transfer roller 1154 transfers (primary transfer) the image formed on the surface of the photoreceptor drum 1151 onto the transfer belt 117 in contact with the photoreceptor drum 1151 .

A cleaner 1155 removes the recording material D remaining on the surface of the photosensitive drum 1151 .
A charge removal lamp 1156 removes charges remaining on the surface of the photosensitive drum 1151 .

The optical scanning device 116 is also called an LSU (laser scanning unit). The optical scanning device 116 forms an electrostatic latent image on the surface of the photoreceptor drum 1151 of each image forming unit 115 by controlling the beam B according to input image data under the control of the processor 141 . The image data input here is, for example, image data read from a document or the like by the scanner 102 . Alternatively, the image data input here is image data transmitted from another device or the like and received by image forming apparatus 100 .

The beam B emitted by the optical scanning device 116 to the image forming unit 115Y is the beam BY, the beam B applied to the image forming unit 115M is the beam BM, the beam B applied to the image forming unit 115C is the beam BC, and the image forming unit 115K is the beam B. Let the beam B irradiating to be referred to as a beam BK. Therefore, the optical scanning device 116 controls the beam BY according to the Y (yellow) component of the image data. The optical scanning device 116 controls the beam BM according to the M (magenta) component of the image data. The optical scanning device 116 controls the beam BC according to the C (cyan) component of the image data. The optical scanning device 116 controls the beam BK according to the K (key) component of the image data. Optical scanning device 116 is further described below.

The transfer belt 117 is, for example, an endless belt, and is rotatable by the action of rollers. The transfer belt 117 conveys the image transferred from each image forming unit 115 to the position of the secondary transfer roller 118 by rotating.

The secondary transfer roller 118 has two rollers facing each other. The secondary transfer roller 118 transfers (secondary transfer) the image formed on the transfer belt 117 onto the image forming medium P passing between the secondary transfer rollers 118 .

The fixing section 119 heats and presses the image forming medium P onto which the image has been transferred. As a result, the image transferred onto the image forming medium P is fixed. The fixing section 119 includes a heating section 1191 and a pressure roller 1192 facing each other.

The heating unit 1191 is, for example, a roller provided with a heat source for heating the heating unit 1191 . The heat source is, for example, a heater. A roller heated by a heat source heats the imaging medium P. As shown in FIG.
Alternatively, the heating section 1191 may comprise an endless belt suspended over a plurality of rollers. For example, the heating unit 1191 includes a plate heat source, an endless belt, belt conveying rollers, tension rollers and press rollers. The endless belt is, for example, a film-like member. A belt conveying roller drives an endless belt. A tension roller applies tension to the endless belt. The press roller has an elastic layer formed on its surface. The heat generating portion of the plate heat source contacts the inner side of the endless belt and is pressed in the direction of the press roller, thereby forming a fixing nip of a predetermined width with the press roller. Due to the configuration in which the plate-shaped heat source heats while forming a nip region, the responsiveness at the time of energization is higher than in the case of the heating method using a halogen lamp.

The pressure roller 1192 presses the image forming medium P passing between the pressure roller 1192 and the heating section 1191 .

The double-sided unit 120 puts the image forming medium P into a state in which the back side can be printed. For example, the duplex unit 120 turns over the image forming medium P by switching back the image forming medium P using a roller or the like.
The paper discharge tray 121 is a platform from which the image forming medium P after printing is discharged.

A scanner 102 is a device having a scanning function. The scanner 102 is, for example, an optical reduction type that includes an imaging device such as a CCD (charge-coupled device) image sensor. Alternatively, the scanner 102 is of a contact image sensor (CIS) type having an imaging device such as a CMOS (complementary metal-oxide-semiconductor) image sensor. Alternatively, scanner 102 may be of any other known type. A scanner 102 reads an image from a document or the like. The scanner 102 has a reading module 131 and a document feeder 132 .

The reading module 131 converts incident light into a digital signal using an image sensor. Thereby, the reading module 131 reads an image from the surface of the document.

The document feeder 132 is also called, for example, an ADF (auto document feeder). The document feeder 132 successively conveys documents placed on a document tray. An image of the transported document is read by the scanner 102 . Also, the document feeder 132 may include a scanner for reading an image from the back side of the document. Note that the surface from which the image is read by the scanner 102 is the front surface.

The operation panel 103 includes a man-machine interface for input/output between the image forming apparatus 100 and an operator of the image forming apparatus 100 . The operation panel 103 includes, for example, a touch panel 1031, an input device 1032, and the like.

The touch panel 1031 is, for example, a laminate of a display such as a liquid crystal display or an organic EL display and a pointing device for touch input. A display included in touch panel 1031 functions as a display device that displays a screen for notifying an operator of image forming apparatus 100 of various types of information. Also, the touch panel 1031 functions as an input device that receives a touch operation by the operator.

Input device 1032 receives an operation by an operator of image forming apparatus 100 . Input device 1032 is, for example, a keyboard, keypad, or touchpad.

Next, the main circuit configuration of the image forming apparatus 100 will be described with reference to FIG. FIG. 3 is a block diagram showing an example of the main circuit configuration of the image forming apparatus 100. As shown in FIG. The image forming apparatus 100 includes, for example, a processor 141, a ROM (read-only memory) 142 , a RAM (random-access memory) 143 , an auxiliary storage device 144, a communication interface 145, a printer 101, a scanner 102, and an operation panel 103. . A bus 146 or the like connects these units.

The processor 141 corresponds to a central portion of a computer that performs processing such as calculation and control required for the operation of the image forming apparatus 100 . Processor 141 controls each unit to realize various functions of image forming apparatus 100 based on programs such as system software, application software, and firmware stored in ROM 142 or auxiliary storage device 144 . Note that part or all of the program may be incorporated in the circuit of the processor 141 . The processor 141 includes, for example, a CPU (central processing unit), MPU (micro processing unit), SoC (system on a chip), DSP (digital signal processor), GPU (graphics processing unit), ASIC (application specific integrated circuit), Examples include PLDs (programmable logic devices) and FPGAs (field-programmable gate arrays). Alternatively, processor 141 is a combination of several of these.

The ROM 142 corresponds to the main memory of a computer having the processor 141 as its core. The ROM 142 is a non-volatile memory exclusively used for reading data. The ROM 142 stores, for example, firmware among the above programs. In addition, the ROM 142 stores data or various setting values that the processor 141 uses when performing various processes.

The RAM 143 corresponds to the main memory of a computer having the processor 141 as its core. The RAM 143 is a memory used for reading and writing data. The RAM 143 is used as a so-called work area for storing data temporarily used when the processor 141 performs various processes. RAM 143 is, for example, a volatile memory.

The auxiliary storage device 144 corresponds to an auxiliary storage device of a computer having the processor 141 as its core. The auxiliary storage device 144 is, for example, an EEPROM (electric erasable programmable read-only memory), HDD (hard disk drive), SSD (solid state drive), or eMMC (embedded MultiMediaCard). The auxiliary storage device 144 stores, among the above programs, system software and application software, for example. In addition, the auxiliary storage device 144 stores data used by the processor 141 to perform various processes, data generated by the processes performed by the processor 141, various setting values, and the like. Note that the image forming apparatus 100 may include an interface into which a storage medium such as a memory card or USB (universal serial bus) memory can be inserted as the auxiliary storage device 144 . The interface reads and writes information to the storage medium.

Communication interface 145 is an interface for image forming apparatus 100 to communicate via a network or the like.

A bus 146 includes a control bus, an address bus, a data bus, etc., and transmits signals exchanged with each part of the image forming apparatus 100 .

The optical scanning device 116 will be further described below with reference to FIGS. 4 to 7 and the like. FIG. 4 is a diagram showing an example of the optical scanning device 116. As shown in FIG. FIG. 5 is a plan view of an example of the optical system of the optical scanning device 116 . FIG. 6 is a partial enlarged view partially enlarging the essential part of FIG. 7 is a side view of the structure of FIG. 6. FIG. The optical scanning device 116 includes, for example, a polygon mirror 151, a motor 152, a light source 153 and a plurality of optical elements.

The polygon mirror 151 is a mirror (deflector) in the shape of a regular polygon, each side of which is a reflecting surface 1511 that reflects the laser. The polygon mirror 151 shown in FIGS. 4 to 7 is, for example, a regular heptagonal mirror having seven side surfaces (reflecting surfaces 1511). A reflecting surface 1511 provided on the polygon mirror 151 is continuous along the rotation direction CCW (counterclockwise direction in FIG. 5) of the polygon mirror 151 and constitutes the outer peripheral surface of the polygon mirror 151 . The polygon mirror 151 is rotatable around a rotation axis parallel to each reflecting surface 1511 . Also, the rotation axis of the polygon mirror 151 is orthogonal to the rotation axis of each photosensitive drum 1151 . 6 is a plane perpendicular to the rotation axis of the polygon mirror 151. As shown in FIG.

The optical scanning device 116 can be equipped with a plurality of types of polygon mirrors 151 having different numbers of reflecting surfaces 1511 . For example, the optical scanning device 116 can be equipped with an octagonal prism-shaped polygon mirror 151 having eight reflecting surfaces 1511, in addition to the regular heptagonal prism-shaped polygon mirror 151 shown in FIGS. Also, the optical scanning device 116 may be capable of mounting a polygon mirror 151 having six or less or nine or more faces. However, it is preferable that the polygon mirrors 151 attached to the optical scanner 116 have the same inscribed circle radius and the same rotation axis. By using the polygon mirrors 151 having the same inscribed circle radius and the same rotation axis, the beam B can be reflected on the same surface without changing the optical path length regardless of the number of polygon mirror surfaces. This is because it is possible to suppress focal position fluctuations on the plane.
When it is necessary to distinguish the number of faces of the polygon mirror 151, the polygon mirror 151 with seven faces is denoted by polygon mirror 151-7, and the polygon mirror 151 with eight faces is denoted by 151-8. shall be appended with "- number of faces".

A motor 152 rotates the polygon mirror 151 in the rotation direction CCW at a predetermined speed. The rotation axis of the motor 152 and the rotation axis of the polygon mirror 151 are, for example, coaxial. However, the rotating shaft of the motor 152 and the rotating shaft of the polygon mirror 151 do not have to be coaxial.

The light source 153 emits a beam B such as laser light. Light source 153 comprises, for example, a plurality of laser diodes. That is, beam B is a multi-beam composed of beams emitted from a plurality of laser diodes. Note that the plurality of laser diodes have distances in the main scanning direction. Therefore, each beam included in beam B also has a distance in the main scanning direction. The optical scanning device 116 includes, for example, four light sources 153: a light source 153C, a light source 153M, a light source 153Y, and a light source 153K. For example, the light source 153Y emits a beam BY corresponding to the Y component, the light source 153M emits a beam BM corresponding to the M component, the light source 153C emits a beam BC corresponding to the C component, and the light source 153K emits a beam corresponding to the K component. A corresponding beam BK is emitted.
The optical scanning device 116 irradiates each beam B onto the surface of each photosensitive drum 1151 through an optical path formed by a predetermined scanning optical system provided for each beam B. FIG. The scanning optical system includes multiple optical elements. As an example, as shown in FIGS. 4 and 5, the optical scanning device 116 has two beams B as one set, and a pair of scanning optical systems are arranged on the left and right sides of the polygon mirror 151 . That is, as shown in FIGS. 4 and 5, the optical scanning device 116 has two scanning optical systems 161 and 161 each including a plurality of optical elements on both sides (left and right sides in the drawing) of a single polygon mirror 151. It has a scanning optical system 162 . Note that the polygon mirror 151 is included in each of the scanning optical system 161 and the scanning optical system 162 . That is, the polygon mirrors 151 included in each of the scanning optical system 161 and scanning optical system 162 are the same polygon mirror 151 .

The scanning optical system 161 on the left side of the drawing includes a scanning optical system that scans the beam BY and a scanning optical system that scans the beam BM. The scanning optical system 161 reflects the beam BY emitted from the light source 153Y and the beam BM emitted from the light source 153M on the same reflecting surface 1511 of the polygon mirror 151 rotating in the rotation direction CCW. Thereby, the beam BY and the beam BM are deflected in the main scanning direction along the rotation direction CCW, and scan the surfaces of the two photosensitive drums 1151Y and 1151M, respectively. The scanning optical system 161 includes a polygon mirror 151, a light source 153Y, a light source 153M, a pre-deflection optical system 170Y, a pre-deflection optical system 170M, and a post-deflection optical system 180YM. The pre-deflection optical system 170Y is an optical system for the beam BY. Also, the pre-deflection optical system 170M is an optical system for the beam BM. Further, the post-deflection optical system 180YM is an optical system for beam BY and beam BM.
Note that the beam BY is an example of the first light flux. Also, the beam BM is an example of a second light flux. The light source 153Y that emits the beam BY that is the first light flux is an example of the first light source. The light source 153M that emits the beam BM that is the second light flux is an example of the second light source.

Here, the direction in which each beam B is deflected (scanned) by the polygon mirror 151 as a deflector (the circumferential direction of the polygon mirror 151) is defined as the "main scanning direction". Further, a direction orthogonal to the main scanning direction and orthogonal to the optical axis direction of the beam B is defined as the "sub-scanning direction" of the beam B. FIG. 5 and 6, the rotation axis direction of the polygon mirror 151 is the sub-scanning direction. 5 and 6, the main scanning direction of the beam B is the direction orthogonal to the rotation axis direction of the polygon mirror 151 and the direction orthogonal to the optical axis direction of the beam B. In FIGS.

The scanning optical system 162 on the right side of the drawing includes a scanning optical system for scanning the beam BC and a scanning optical system for scanning the beam BK. The scanning optical system 162 reflects the beam BC emitted from the light source 153C and the beam BK emitted from the light source 153K by the same reflecting surface 1511 of the polygon mirror 151 rotating in the rotation direction CCW. As a result, the beams BC and BK are deflected in the main scanning direction along the rotation direction CCW, and scan the surfaces of the two photosensitive drums 1151C and 1151K, respectively. The scanning optical system 162 includes a polygon mirror 151, a light source 153C, a light source 153K, a pre-deflection optical system 170C, a pre-deflection optical system 170K, and a post-deflection optical system 180CK.
Note that the beam BK is an example of the first light flux. Also, the beam BC is an example of a second light flux. The light source 153K that emits the beam BK that is the first light flux is an example of the first light source. The light source 153C that emits the beam BC that is the second light flux is an example of the second light source.

Here, the polygon mirror 151, the light source 153, and the pre-deflection optical system 170 will be further described by taking the scanning optical system 161 on the left side of the drawing as an example. The polygon mirror 151 rotates while reflecting on the same reflecting surface 1511 the two beams B, the beam BY emitted from the light source 153Y and the beam BM emitted from the light source 153M. As a result, two image planes arranged at predetermined positions, that is, the surfaces of the corresponding photosensitive drums 1151Y and 1151M are scanned at a predetermined linear velocity in the main scanning direction (rotational axis direction of the photosensitive drum 1151). Scan. At this time, the image forming apparatus 100 rotates the photoreceptor drum 1151Y and the photoreceptor drum 1151M in the sub-scanning direction. As a result, an electrostatic latent image corresponding to the Y component is formed on the surface of the photosensitive drum 1151Y. Also, an electrostatic latent image corresponding to the M component is formed on the surface of the photosensitive drum 1151M.

As shown in FIGS. 5 and 6, the light source 153Y and the light source 153M of the scanning optical system 161 are arranged at different angular positions when viewed from the front side of the paper. That is, the two light sources 153Y and 153M are arranged such that the directions in which the beam BY and the beam BM are incident on the reflecting surface 1511 have a divergence angle θ. In other words, the two light sources 153Y and 153M are arranged such that the beam BY and the beam BM have an opening angle θ in the main scanning direction. Also, the light source 153Y of the two light sources 153 is located downstream of the light source 153M along the rotation direction CCW of the polygon mirror 151. As shown in FIG. On the other hand, the light source 153M is upstream of the light source 153Y along the rotation direction CCW.

Also, as shown in FIG. 7, the two light sources 153Y and 153M are positioned slightly shifted in the sub-scanning direction. The light source 153M is positioned higher than the light source 153Y. That is, the light source 153M is closer to the front side of the plane of FIGS. 5 and 6 than the light source 153Y. Also, the optical axes (light traveling directions) of the pre-deflection optical system 170Y and the pre-deflection optical system 170M are perpendicular to the rotation axis 131b of the polygon mirror 151. FIG. Therefore, the beam BY and the beam BM emitted from the light source 153Y and the light source 153M are incident on the same reflecting surface 1511 at slightly shifted positions in the sub-scanning direction.

The scanning optical system 161 includes a pre-deflection optical system 170 on each optical path between the light source 153 and the polygon mirror 151 . That is, the scanning optical system 161 includes two pre-deflection optical systems 170, a pre-deflection optical system 170Y and a pre-deflection optical system 170M. The pre-deflection optical system 170 Y is arranged on the optical path between the light source 153 Y and the polygon mirror 151 . The pre-deflection optical system 170M is arranged on the optical path between the light source 153M and the polygon mirror 151. FIG. Each pre-deflection optical system 170 includes a collimator lens 171 , a sub-scanning diaphragm 172 , a cylinder lens 173 and a main scanning diaphragm 174 . The pre-deflection optical system 170Y includes a collimator lens 171Y, a sub-scanning diaphragm 172Y, a cylinder lens 173Y and a main scanning diaphragm 174YM. Also, the pre-deflection optical system 170M includes a collimator lens 171M, a sub-scanning diaphragm 172M, a cylinder lens 173M and a main scanning diaphragm 174YM. Note that the collimator lens 171Y and the collimator lens 171M are the collimator lens 171. FIG. Also, the sub-scanning diaphragm 172Y and the sub-scanning diaphragm 172M are the sub-scanning diaphragm 172. FIG. The cylinder lens 173Y and the cylinder lens 173M are the cylinder lens 173. As shown in FIG. Further, the main scanning diaphragm 174YM is the main scanning diaphragm 174 for beam BY and beam BM. The main scanning diaphragm 174YM included in each of the pre-deflection optical system 170Y and the pre-deflection optical system 170M is the same main scanning diaphragm 174YM.

The collimator lens 171 gives a predetermined convergence to the beam B emitted from the light source 153 . A collimator lens 171 makes the beam B parallel.

The sub-scanning diaphragm 172 shapes the shape of the beam B that has passed through the collimator lens 171 in the sub-scanning direction. For example, the sub-scanning diaphragm 172 shapes the width of the beam B in the sub-scanning direction to a predetermined width.

The cylinder lens 173 gives a predetermined convergence in the sub-scanning direction to the beam B that has passed through the sub-scanning diaphragm 172 . As a result, the beam B that has passed through the cylinder lens 173 has a narrower width in the sub-scanning direction as it approaches the reflecting surface 1511 . Therefore, a plurality of beams B can be incident on the same reflecting surface 1511 at positions shifted in the sub-scanning direction so as not to overlap each other.

The main scanning diaphragm 174 shapes the shape of the beam B that has passed through the cylinder lens 173 in the main scanning direction. For example, the main scanning diaphragm 174 shapes the width of the beam B in the main scanning direction to a predetermined width. Main scanning diaphragm 174 will be further described later. Note that the main scanning diaphragm 174 is an example of a third diaphragm.

Furthermore, the polygon mirror 151, the light source 153, and the pre-deflection optical system 170 of the scanning optical system 162 on the right side of the drawing will also be described. The polygon mirror 151 rotates while reflecting on the same reflecting surface 1511 the two beams B, the beam BC emitted from the light source 153C and the beam BK emitted from the light source 153K. As a result, two image planes arranged at predetermined positions, that is, the surfaces of the corresponding photosensitive drums 1151C and 1151K are scanned at a predetermined linear velocity in the main scanning direction (rotational axis direction of the photosensitive drum 1151). Scan. At this time, the image forming apparatus 100 rotates the photosensitive drums 1151C and 1151K in the sub-scanning direction. As a result, an electrostatic latent image corresponding to the C component is formed on the surface of the photosensitive drum 1151C. Also, an electrostatic latent image corresponding to the K component is formed on the surface of the photosensitive drum 1151K.

The two light sources 153C and 153K of the scanning optical system 162 are arranged at different angular positions when viewed from the front side of the paper surface of FIGS. . That is, the two light sources 153C and 153K are arranged such that the directions in which the beams BC and BK are incident on the reflecting surface 1511 have an opening angle θ. In other words, the two light sources 153C and 153K are arranged such that the beams BC and BK have an opening angle θ in the main scanning direction. In addition, the light source 153C of the two light sources is located upstream of the light source 153K along the rotation direction CCW of the polygon mirror 151 . On the other hand, the light source 153K is downstream from the light source 153C along the rotation direction CCW.

Also, the light source 153C and the light source 153K are positioned slightly shifted in the sub-scanning direction. Light source 153C is positioned higher than light source 153K. Therefore, the beams BC and BK emitted from the light sources 153C and 153K are incident on the same reflecting surface 1511 at slightly shifted positions in the sub-scanning direction.

The scanning optical system 162 includes a pre-deflection optical system 170 on each optical path between the light source 153 and the polygon mirror 151 . That is, the scanning optical system 162 includes two pre-deflection optical systems 170, a pre-deflection optical system 170C and a pre-deflection optical system 170K. The pre-deflection optical system 170C is arranged on the optical path between the light source 153C and the polygon mirror 151. FIG. The pre-deflection optical system 170K is arranged on the optical path between the light source 153K and the polygon mirror 151. FIG. The pre-deflection optical system 170C includes a collimator lens 171C, a sub-scanning diaphragm 172C, a cylinder lens 173C and a main scanning diaphragm 174CK. The pre-deflection optical system 170K includes a collimator lens 171K, a sub-scanning diaphragm 172K, a cylinder lens 173K and a main scanning diaphragm 174CK. Note that the collimator lens 171C and the collimator lens 171K are the collimator lens 171 . Also, the sub-scanning diaphragm 172C and the sub-scanning diaphragm 172K are the sub-scanning diaphragm 172. As shown in FIG. The cylinder lens 173C and the cylinder lens 173K are the cylinder lens 173. As shown in FIG. Further, the main scanning diaphragm 174CK is the main scanning diaphragm 174 . The main scanning diaphragm 174CK included in each of the pre-deflection optical system 170C and the pre-deflection optical system 170K is the same main scanning diaphragm 174CK. As described above, the scanning optical system 162 has components similar to those of the scanning optical system 161 .

Next, the post-deflection optical system 180 will be described. The post-deflection optical system 180 guides the beam B reflected by the reflecting surface 1511 to the surface of the photosensitive drum 1151 . The optical scanning device 116 includes two post-deflection optical systems 180, a post-deflection optical system 180YM and a post-deflection optical system 180CK. The post-deflection optical system 180 includes an f.theta. lens 181, an f.theta.

The f.theta.
One upstream fθ lens 181 near the polygon mirror 151 is provided for one post-deflection optical system 180 . That is, the f-theta lens 181 is in the optical path of the pair of two beams B. FIG. A set of two beams B passes through the same fθ lens 181 . For example, the fθ lens 181YM is located on the optical path of the beam BY and on the optical path of the beam BM. The beam BY and the beam BM pass through the fθ lens 181YM.

One fθ lens 182 on the downstream side close to the photosensitive drum 1151 is shown for each post-deflection optical system 180 in FIG. However, the f.theta. lens 182 is provided independently on each optical path of each beam B as shown in FIG . The fθ lens 182YM shown in FIG. 5 collectively shows the fθ lens 182Y and the fθ lens 182M shown in FIG . The fθ lens 182CK shown in FIG. 5 collectively shows the fθ lens 182C and the fθ lens 182K shown in FIG . lens 182Y, f.theta. lens 182M, f.theta. lens 182C, and f.theta. Each beam B passes through the fθ lens 182 on each optical path. The fθ lenses 182 are positioned near a third cover glass 193 to be described later.

Photodetectors 183 are at the ends of the start of scanning of beam B (scan position AA and scan position AB). A photodetector 183 is provided for adjusting the horizontal synchronization of the beam B that has passed through the f-theta lens 181 and the f-theta lens 182 .

A folding mirror 184 is on the optical path from the fθ lens 182 to the photodetector 183 . Folding mirror 184 reflects beam B to fold it back toward photodetector 183 . However, in FIG. 5, the optical path of the beam B and the photodetector 183, folding mirror 184, and optical path correction element 185 on the optical path are shown in a plane.

The optical path correction element 185 is on the optical path between the folding mirror 184 and the photodetector 183 . The optical path correction element 185 guides the beam B reflected by the folding mirror 184 onto the detection surface of the photodetector 183 .

The folding mirrors 186 to 188 are a plurality of mirrors that reflect the beam B that has passed through the fθ lens 181 and fold it toward the surface of each photosensitive drum 1151 . The optical scanning device 116 includes two folding mirrors 186, a folding mirror 186YM and a folding mirror 186CK. The optical scanning device 116 includes four folding mirrors 187: a folding mirror 187Y, a folding mirror 187M, a folding mirror 187C, and a folding mirror 187K. The optical scanning device 116 includes two folding mirrors 188, a folding mirror 188Y and a folding mirror 188K. 5, illustration of the folding mirrors 186 to 188 is omitted.

The optical scanning device 116 also includes a first cover glass 191 , a second cover glass 192 , and a third cover glass 193 .

A first cover glass 191 is between the pre-deflection optics 170 and the polygon mirror 151 . A second cover glass 192 is between the polygon mirror 151 and the post-deflection optics 180 . The first cover glass 191 and the second cover glass 192 are provided to prevent wind noise when the polygon mirror 151 rotates. The first cover glass 191 prevents the wind noise from leaking from the beam B entrance. The second cover glass 192 prevents the wind noise from leaking out of the beam B exit.

A third cover glass 193 is between the fθ lens 182 and the photosensitive drum 1151 . A third cover glass 193 covers the exit from which the beam B is emitted in the housing of the optical scanning device 116 .

As described above, the optical scanning device 116 has the scanning optical system 161 and the scanning optical system 162 arranged on the left and right with the polygon mirror 151 at the center. Therefore, in the optical scanning device 116, when the polygon mirror 151 is rotated in a certain direction, the scanning direction of the photosensitive drum 1151 by the scanning optical system 161 and the scanning direction of the photosensitive drum 1151 by the scanning optical system 162 are reversed. . Here, in FIG. 5, the side where the light source 153Y, the light source 153M, the light source 153C, and the light source 153K are drawn with the polygon mirror 151 as the center (upper side of the paper surface) is assumed to be the positive side, and the opposite side (lower side of the paper surface) is the negative side. Assume. In this case, the scanning optical system 161 scans the image plane from the plus side indicated by the arrow S to the minus side. On the other hand, the scanning optical system 162 scans the image plane from the minus side indicated by the arrow T to the plus side.

The main scanning diaphragm 174 will be described with reference to FIGS. 8 and 9. FIG.
8 and 9 show a main scanning diaphragm 174a and a main scanning diaphragm 174b as examples of the main scanning diaphragm 174. FIG. 8 and 9 are diagrams showing examples of the main scanning diaphragm 174, respectively. The main scanning diaphragm 174 shown in FIGS. 8 and 9 is the main scanning diaphragm 174YM. The main scanning diaphragm 174 shown in FIGS. 8 and 9 is a plan view of the main scanning diaphragm 174 viewed from the side where the light source 153 is located. The main scanning diaphragm 174 shown in FIGS. 8 and 9 is a plan view of the main scanning diaphragm 174 in FIG. 6 as seen from the arrow U direction.

The main scanning diaphragm 174 is a plate-like member. The main scanning diaphragm 174 has an aperture 175 . Note that the main scanning diaphragm 174a shown in FIG. 8 has an opening 175a as an example of the opening 175. As shown in FIG. The main scanning diaphragm 174b shown in FIG. 9 has an opening 175b as an example of the opening 175. As shown in FIG. The opening 175 consists of two openings 176, an opening 176a and an opening 176b. Each opening 176 has a rectangular shape whose width in the sub-scanning direction is larger than the width of the beam B in the sub-scanning direction. The width of the aperture 176 in the sub-scanning direction is such that even if the passing position of the beam B shifts in the sub-scanning direction due to component precision or the like, the side of the beam B in the sub-scanning direction (upper or lower side of the paper) is not blocked. .

8 and 9 show the optical axis OA of the beam B incident on the aperture 176. FIG. 8 and 9 show the optical axis OA of the beam BY as the optical axis OAY, and the optical axis OA of the beam BM as the optical axis OAM. 8 and 9 show an equisecting line EL which is a straight line passing through the optical axis OA and parallel to the sub-scanning direction. In FIGS. 8 and 9, ELY denotes an equal dividing line EL passing through the optical axis OAY, and ELM denotes an equal dividing line EL passing through the optical axis OAM. The equal dividing line EL is a straight line that bisects the beam B in the main scanning direction.

The opening 176a has a length xY1 on the downstream side in the main scanning direction and a length xY2 on the upstream side in the main scanning direction with respect to the equal dividing line ELY. The length relationship of xY1 and xY2 is xY1>xY2. The beam BY passing through the opening 176a has a length xY2 from the optical axis OAY to the upstream end in the main scanning direction, and a length xY1 from the optical axis OAY to the downstream end in the main scanning direction. Therefore, the aperture 176a is an example of a first diaphragm that shapes the beam BY, which is the first light flux. Also, xY2 is an example of the first length. xY1 is an example of the second length.

The opening 176b has a length xM1 on the upstream side in the main scanning direction and a length xM2 on the downstream side in the main scanning direction with respect to the dividing line ELM. The length relationship of xM1 and xM2 is xM1>xM2. The beam BM passing through the opening 176b has a length xM1 from the optical axis OAM to the upstream end in the main scanning direction, and a length xM2 from the optical axis OAY to the downstream end in the main scanning direction. Therefore, the opening 176b is an example of a second diaphragm that shapes the beam BM that is the second light flux. Also, xM1 is an example of the third length. xM2 is an example of a fourth length.

In the opening 175a shown in FIG. 8, the opening 176a and the opening 176b do not overlap. Therefore, the opening 175a consists of two openings 176 that are not connected.
In the opening 175b shown in FIG. 9, the opening 176a and the opening 176b are overlapped. That is, the opening 175b is one opening having a shape in which two openings 176 are connected.

Note that the aperture 176a is an example of a first diaphragm that shapes the beam BY, which is the first light flux. Also, the aperture 176b is an example of a second diaphragm that shapes the beam BM that is the second light flux.

In this way, the optical scanning device 116 of the embodiment can scan both the beams BM and BY in the main scanning direction by one main scanning diaphragm 174 because the beams BM and BY are shifted in the sub-scanning direction. The shape can be trimmed to the desired shape.
Also, as shown in FIG. 8, when the beams BM and BY are sufficiently separated in the sub-scanning direction, the openings 176a and 176b can be individually arranged so as not to overlap. On the other hand, as shown in FIG. 9, when the distance between the beams BM and BY in the sub-scanning direction is small, the apertures 176a and 176b overlap. It should be noted that the width of the polygon mirror 151 in the sub-scanning direction must be increased as the beam BM and the beam BY are separated from each other in the sub-scanning direction. The smaller the width of the polygon mirror 151 in the sub-scanning direction, the more compact the optical scanning device 116 can be. Also, the smaller the width of the polygon mirror 151 in the sub-scanning direction, the shorter the time it takes for the polygon mirror 151 to rotate stably at a specified rotation speed from the start of rotation. Furthermore, the smaller the width of the polygon mirror 151 in the sub-scanning direction, the shorter the time during which the rotation of the polygon mirror 151 is stopped.

A main scanning diaphragm 200 used as a comparison target for the main scanning diaphragm 174 will be described with reference to FIG. Note that the main scanning diaphragm 200 shown in FIG. 10 is the main scanning diaphragm 200YM. The main scanning diaphragm 200YM is a main scanning diaphragm for the beam BY and the beam BM, like the main scanning diaphragm 174YM. The main scanning diaphragm 200 has an opening 201 instead of the opening 175 of the main scanning diaphragm 174 . The opening 201 has two openings 202 , 202 a and 202 b , instead of the openings 176 a and 176 b of the opening 175 . The opening 202a and the opening 202b have the same length on the upstream side in the main scanning direction and the length on the downstream side in the main scanning direction with respect to the dividing line EL. As an example, the opening 202a has a length xY1 on the downstream side in the main scanning direction and a length xY1 on the upstream side in the main scanning direction with respect to the dividing line ELY. The opening 202b has a length xM1 on the upstream side in the main scanning direction and a length xM2 on the downstream side in the main scanning direction with respect to the dividing line ELM.

Also, it is preferable that the main scanning diaphragm 174 be close to the polygon mirror 151 . As described above, beam B is a multi-beam consisting of a plurality of beams. Each beam included in beam B has a distance in the main scanning direction. Therefore, each beam included in the beam B that has passed through the main scanning diaphragm 174 tends to spread in the main scanning direction as the distance from the main scanning diaphragm 174 increases. When each beam included in beam B spreads in the main scanning direction, each beam tends to pass through a position deviated from the desired optical path. Since each beam deviates from the desired optical path, vignetting is likely to occur when reflected by the polygon mirror 151, and the focus position of each beam is likely to be different, resulting in deterioration of image quality. cause. Therefore, the closer the main scanning diaphragm 174 is to the polygon mirror 151, the more the image quality of the image forming apparatus 100 is improved, for example, the curvature of field is reduced. Therefore, as in the embodiment, the main scanning diaphragm 174 is positioned so that the beam B passes through the main scanning diaphragm 174 behind the cylinder lens 173, thereby improving the image quality of the image forming apparatus 100. FIG. However, the closer the main scanning diaphragm 174 is to the polygon mirror 151, the more the positions of the beam BY and the beam BM in the main scanning direction overlap. For this reason, it becomes difficult to dispose an aperture individually for each beam B like the sub-scanning aperture 172 . By allowing the two beams B, the beam BY and the beam BM, to pass through one main scanning diaphragm 174 as in the embodiment, it is possible to shape the shape in the main scanning direction near the polygon mirror 151 . Become. In the conventional optical scanning device, a diaphragm for shaping both the main scanning direction and the sub-scanning direction is arranged at the same position as the sub-scanning diaphragm 172 .

In addition, the main scanning diaphragm 174a and the main scanning diaphragm 174b have a shape in which an opening 175 is opened in a single integrated plate-like member. Therefore, it is possible to reduce the cost compared to using two main scanning diaphragms.

The main scanning diaphragm 174 will be further described with reference to FIGS. 11 to 18. FIG. 11 to 18 are diagrams for explaining the main scanning diaphragm. 11 to 18, the upstream side of the rotation direction CCW of the polygon mirror 151 is defined as the plus side, and the downstream side is defined as the minus side. 11 to 18 show the image plane IS. The beam B deflected by the polygon mirror 151 scans the image plane IS from the plus side to the minus side. 11 to 18, a portion between the polygon mirror 151 and the image plane IS is omitted. 11 to 18 show the polygon mirror 151-8, the polygon mirror 151-7 is also shown by phantom lines for comparison with the polygon mirror 151-8. It is assumed that the polygon mirror 151-7 and the polygon mirror 151-8 have the same radius of inscribed circle, and the radius of the inscribed circle is D for both.

FIG. 11 is a diagram showing a state in which the beam BM shaped by the main scanning diaphragm 200YM is deflected to the minus side scanning end.
FIG. 12 is a diagram showing a state in which the beam BM shaped by the main scanning diaphragm 200YM is deflected to the plus side scanning end.
As shown in FIGS. 11 and 12, the beam BM shaped by the main scanning diaphragm 200YM has the same width on the upstream side in the main scanning direction from the optical axis OAM and on the downstream side in the main scanning direction from the optical axis OAM. It is assumed that the width of the beam BM shaped by the main scanning diaphragm 200YM on the upstream side in the main scanning direction from the optical axis OAM and the width on the downstream side in the main scanning direction from the optical axis OAM are both x1. As shown in FIGS. 11 and 12, the beam BM is set so that the beam BM shaped by the main scanning diaphragm 200YM is not eclipsed by the polygon mirror 151-7. However, when the polygon mirror 151-8 is used, since the length of one side of the polygon mirror 151-8 is shorter than the length of one side of the polygon mirror 151-7, vignetting VM occurs at the plus side scanning end. That is, part of the beam BM protrudes from the reflecting surface 1511 . On the other hand, at the minus side scanning end, since there is a margin from the position where the beam BM hits the polygon mirror 151-7 to the vertex on the upstream side from the position of the polygon mirror 151-7, vignetting occurs even with the polygon mirror 151-8. has not occurred.

FIG. 13 is a diagram showing a state in which the beam BY shaped by the main scanning diaphragm 200YM is deflected to the minus side scanning end.
FIG. 14 is a diagram showing a state in which the beam BY shaped by the main scanning diaphragm 200YM is deflected to the plus side scanning end.
As shown in FIGS. 13 and 14, the beam BY passing through the main scanning diaphragm 200YM has the same width on the upstream side in the main scanning direction from the optical axis OAY and on the downstream side in the main scanning direction from the optical axis OAY. It is assumed that the width of the beam BM on the upstream side in the main scanning direction from the optical axis OAY and the width on the downstream side in the main scanning direction from the optical axis OAY are both x3. As shown in FIGS. 13 and 14, beam BY is set so that beam BY shaped by main scanning diaphragm 200YM is not eclipsed by polygon mirror 151-7. However, when the polygon mirror 151-8 is used, since the length of one side of the polygon mirror 151-8 is shorter than the length of one side of the polygon mirror 151-7, vignetting VY occurs at the minus scanning end. That is, part of beam BY protrudes from reflecting surface 1511 . On the other hand, at the plus side scanning end, since there is a margin from the position where the beam BY hits the polygon mirror 151-7 to the vertex on the upstream side from the position of the polygon mirror 151-7, vignetting occurs even with the polygon mirror 151-8. has not occurred.

FIG. 15 is a diagram showing a state in which the beam BM shaped by the main scanning diaphragm 174YM is deflected to the minus side scanning end.
FIG. 16 is a diagram showing a state in which the beam BM shaped by the main scanning diaphragm 174YM is deflected to the plus side scanning end.
As shown in FIGS. 15 and 16, the beam BM shaped by the main scanning diaphragm 174YM has a width x1 on the upstream side in the main scanning direction from the optical axis OAM and a width x2 on the downstream side in the main scanning direction from the optical axis OAM. Suppose that Since the angle at which the beam BM is incident on the main scanning diaphragm 174YM is close to vertical, it can be assumed that x1≈xM1 and x2≈=xM2.
x2 is a value smaller than x1. That is, the beam BM shaped by the main scanning diaphragm 174YM has the same width as the beam BM shaped by the main scanning diaphragm 200YM on the upstream side in the main scanning direction from the optical axis OAM. Also, the beam BM shaped by the main scanning diaphragm 174YM has a shorter width on the downstream side in the main scanning direction from the optical axis OAM than the beam BM shaped by the main scanning diaphragm 200YM. Therefore, as shown in FIG. 15, the beam BM shaped by the main scanning diaphragm 174YM, like the beam BM shaped by the main scanning diaphragm 200YM, has polygon mirror 151-7 and polygon mirror 151-7 at the minus side scanning end. No vignetting occurs in any of 151-8. As shown in FIG. 16, unlike the beam BM shaped by the main scanning diaphragm 200YM, the beam BM shaped by the main scanning diaphragm 174YM is eclipsed by both the polygon mirrors 151-7 and 151-8. has not occurred.

FIG. 17 is a diagram showing a state in which the beam BY shaped by the main scanning diaphragm 174YM is deflected to the minus side scanning end.
FIG. 18 is a diagram showing a state in which the beam BY shaped by the main scanning diaphragm 174YM is deflected to the plus side scanning end.
As shown in FIGS. 17 and 18, the beam BY shaped by the main scanning diaphragm 174YM has a width of x3 on the downstream side in the main scanning direction from the optical axis OAY and a width of x4 on the upstream side in the main scanning direction from the optical axis OAY. Suppose that Since the angle at which the beam BY enters the main scanning diaphragm 174YM is close to vertical, it can be assumed that x3≈xY1 and x4≈xY2.
x4 is a value smaller than x3. That is, the beam BY shaped by the main scanning diaphragm 174YM has the same width as the beam BY shaped by the main scanning diaphragm 200YM on the downstream side in the main scanning direction from the optical axis OAY. Further, the beam BY shaped by the main scanning diaphragm 174YM has a shorter width on the upstream side in the main scanning direction from the optical axis OAY than the beam BY shaped by the main scanning diaphragm 200YM. Therefore, as shown in FIG. 17, the beam BY shaped by the main scanning diaphragm 174YM differs from the beam BY shaped by the main scanning diaphragm 200YM at both polygon mirrors 151-7 and 151-8. Vignetting does not occur. Then, as shown in FIG. 18, the beam BY shaped by the main scanning diaphragm 174YM, like the beam BY shaped by the main scanning diaphragm 200YM, has polygon mirrors 151-7 and 151 at the minus side scanning end. Vignetting does not occur in any of -8.

As described above, the optical scanning device 116 uses the main scanning diaphragm 174YM with the lengths xY1, xY2, xM1, and xM2 appropriately set so that vignetting does not occur even when the polygon mirror 151 having different numbers of surfaces is used. can be

Although the main scanning diaphragm 174 has been described above using the main scanning diaphragm 174YM, the main scanning diaphragm 174CK is similar to the main scanning diaphragm 174YM. The main scanning diaphragm 174CK shapes the beams BC and BK in the main scanning direction.

As described above, the image forming apparatus 100 of the embodiment can use polygon mirrors 151 having different numbers of faces. Therefore, in the image forming apparatus 100 of the embodiment, different models using the polygon mirrors 151 having different numbers of faces can use a common housing, so that manufacturing costs can be reduced.

The above embodiment can also be modified as follows.
Instead of the main scanning diaphragm 174, a main scanning diaphragm 210 as shown in FIG. 19 may be provided. FIG. 19 is a diagram showing a modification of the main scanning diaphragm. As for the main scanning diaphragm 210, the main scanning diaphragm 210 for beam BY and beam BM will be described as an example.
The main scanning diaphragm 210 includes a main scanning diaphragm 200 and a second main scanning diaphragm 220 . Note that in FIG. 19, the second main scanning diaphragm 220 is indicated by a thick line for the sake of clarity. The main scanning diaphragm 210 uses a main scanning diaphragm such as the main scanning diaphragm 200, which is not supposed to use a plurality of types of polygon mirrors 151 with different numbers of faces, so that a plurality of types of polygon mirrors 151 can be used. It is what I did.

The main scanning diaphragm 210 is obtained by overlapping the main scanning diaphragm 200 and the second main scanning diaphragm 220 . Note that the main scanning diaphragm 200 and the second main scanning diaphragm 220 may be in close contact with each other, or may have a gap between them. 19, the second main scanning diaphragm 220 is closer to the light source 153 than the main scanning diaphragm 200 is. However, the second main scanning diaphragm 220 may be located farther from the light source 153 than the main scanning diaphragm 200 is.

The second main scanning diaphragm 220 has an opening 221 and projections 222 .
Aperture 221 includes an aperture for shaping beam BY and an aperture for shaping beam BM. The aperture for shaping the beam BY has a length of xY1 or more on the downstream side in the main scanning direction and a length of xY2 on the upstream side in the main scanning direction with respect to the equal dividing line ELY. The opening for shaping the beam BM has a length of xM1 or more on the upstream side in the main scanning direction and a length of xM2 on the downstream side in the main scanning direction with respect to the dividing line ELM. Incidentally, as described above, xY1>xY2 and xM1>xM2.

Also, the second main scanning diaphragm 220 is attached to a fixed member 230, for example. The fixing member 230 has a groove 231 for fitting the protrusion 222 . The projection 222 and the groove 231 determine the position of the second main scanning diaphragm in the main scanning direction by fitting the projection 222 into the groove 231 . Also, the projection 222 and the groove 231 fix the second main scanning diaphragm to prevent it from moving in the main scanning direction.
Also, the position of the second main scanning diaphragm 220 in the sub-scanning direction is determined by the contact of the bottom 223a and the bottom 223b of the second main scanning diaphragm 220 with the upper surface of the fixed member 230. FIG.

Therefore, the main scanning diaphragm 200 shapes the shape of the beam BY on the downstream side in the main scanning direction and the shape of the beam BM on the upstream side in the main scanning direction into desired shapes. The second main scanning diaphragm 220 shapes the shape of the beam BY on the upstream side in the main scanning direction and the shape of the beam BM on the downstream side in the main scanning direction into desired shapes. As a result, the beam B shaped by the main scanning diaphragm 210 has the same shape as the beam shaped by the main scanning diaphragm 174, and vignetting can be prevented.

The optical scanning device using the main scanning diaphragm 210 is used with the main scanning diaphragm 210 attached when using the polygon mirror 151-8, and with the main scanning diaphragm 210 removed when using the polygon mirror 151-7. be able to. As a result, the amount of light when using the polygon mirror 151-7 can be made higher than the amount of light when using the polygon mirror 151-8.

Note that the portion of the main scanning diaphragm 200 that shapes the downstream side of the beam BY in the main scanning direction is an example of the first portion. A portion of the main scanning diaphragm 200 that shapes the upstream side of the beam BM in the main scanning direction is an example of a fourth portion. The main scanning diaphragm 200 is an example of a first member including a first portion and a fourth portion.
A portion of the second main scanning diaphragm 220 that shapes the upstream side of the beam BY in the main scanning direction is an example of a third portion. A portion of the second main scanning diaphragm 220 that shapes the downstream side of the beam BM in the main scanning direction is an example of a third portion. The second main scanning diaphragm 220 is an example of a second member including a second portion and a third portion.

In the above-described embodiment, the main scanning diaphragm 174 has a shape in which an opening 175 is opened in an integrated member. However, the main scanning diaphragm 174 may be divided into two or more members.
FIG. 20 shows a main scanning diaphragm 174c as an example of the main scanning diaphragm 174 divided into two or more members. FIG. 20 is a diagram showing an example of the main scanning diaphragm 174. As shown in FIG. The main scanning diaphragm 174 c has an opening 175 c as an example of the opening 175 . The opening 175c does not overlap the opening 176a and the opening 176b. Therefore, the opening 175c consists of two openings 176 that are not connected. Also, the main scanning diaphragm 174d is divided into two members in the sub-scanning direction. That is, the main scanning diaphragm 174c is composed of two members, a member 157a having an opening 176a and a member 157b having an opening 176b.

Further, FIG. 21 shows a main scanning diaphragm 174d as an example of the main scanning diaphragm 174 divided into two or more members. FIG. 21 is a diagram showing an example of the main scanning diaphragm 174. As shown in FIG. The main scanning diaphragm 174 d has an opening 175 d as an example of the opening 175 . The opening 175d overlaps the opening 176a and the opening 176b. That is, the opening 175d is one opening having a shape in which two openings 176 are connected. Also, the main scanning diaphragm 174d is divided into two members in the main scanning direction. That is, the main scanning diaphragm 174d is divided into two members by the opening 175d because the width in the subscanning direction is equal to or less than the width in the subscanning direction of the aperture. A part of the opening 175d in the sub-scanning direction is open without a member that blocks light.

In the above embodiment, the shape of opening 176 is rectangular. However, the shape of the opening 176 may be a shape other than a rectangle.

In the above-described embodiment, the optical scanning device 116 has an arrangement in which two sets of the photosensitive drums 1151 and the light sources 153 of each color are divided into left and right with the polygon mirror 151 interposed therebetween. However, the optical scanning device of the embodiment may arrange three or more photosensitive drums 1151 and light sources 153 on one side of the polygon mirror 151 . In this case, three or more beams B are reflected by the same reflecting surface 1511 . FIG. 22 shows an example of the shape of the main scanning diaphragm when four beams B are reflected by the same reflecting surface. FIG. 22 is a diagram showing a modification of the main scanning diaphragm. A main scanning diaphragm 300 shown in FIG. 22 has an aperture 301 . The opening 301 is one opening having a shape in which the four openings 301 of openings 302a to 302d are connected. Each opening 302 has a rectangular shape whose width in the sub-scanning direction is larger than the width of the beam B in the sub-scanning direction. The openings 302a and 302b are connected by partially overlapping each other. The openings 302b and 302c are connected by partially overlapping each other. The openings 302c and 302d are connected by partially overlapping each other. However, at least one combination of openings 302a and 302b, openings 302b and 302c, and openings 302c and 302d need not overlap. In this case, the opening 301 is an opening made up of a plurality of unconnected openings. The beam B passes through each of the apertures 302a to 302d. That is, the beam Ba passes through the aperture 302a, the beam Bb passes through the aperture 302b, the beam Bc passes through the aperture 302c, and the beam Bd passes through the aperture 302d. As a result, the apertures 302a to 302d shape the shapes of the passing beams Ba to Bd in the main scanning direction.

The opening 302a has a length xa1 on the downstream side in the main scanning direction and a length xa2 on the upstream side in the main scanning direction with respect to the dividing line ELa passing through the optical axis OAa of the beam Ba.
The aperture 302b has a length xb1 on the downstream side in the main scanning direction and a length xb2 on the upstream side in the main scanning direction with respect to the dividing line ELb passing through the optical axis OAb of the beam Bb.
The aperture 302c has a length xc1 on the upstream side in the main scanning direction and a length xc2 on the upstream side in the main scanning direction with respect to the dividing line ELc passing through the optical axis OAc of the beam Bc.
The aperture 302d has a length xd1 on the upstream side in the main scanning direction and a length xd2 on the downstream side in the main scanning direction with respect to the dividing line ELd passing through the optical axis OAd of the beam Bd.

xa1 and xa2 have a relationship of xa1>xa2. xd1 and xd2 have a relationship of xd1>xd2.
Also, xb1, xb2, xc1 and xc2 have the relationships of xb1≧xb2 and xc1≧xc2, for example. Alternatively, xb1, xb2, xc1 and xc2 have the relationships xb1≦xb2 and xc1≧xc2. Alternatively, xb1, xb2, xc1 and xc2 have a relationship of xb1≧xb2 and xc1≦xc2.

In the above embodiment, the image forming apparatus 100 uses four types of printing materials corresponding to the four colors of CMYK. However, the image forming apparatus of the embodiment may use two types, three types, or five or more types of recording materials. In this case, the image forming apparatus of the embodiment includes, for example, the same photosensitive drums 1151 and light sources 153 as the types of recording materials.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.
The invention described in the scope of claims at the time of filing of the present application will be additionally described below.
[1]
a first light source that emits a first light flux;
a second light source that emits a second light beam having an opening angle with respect to the first light beam in the main scanning direction and that exists upstream of the first light source in the main scanning direction;
For the first light flux, the length from the optical axis to the upstream end in the main scanning direction is the first length, and the length from the optical axis to the downstream end in the main scanning direction is greater than the first length. a first diaphragm for shaping the shape of the first light beam so that it has a second length that is greater than the
The shape of the second light beam is set so that the length from the optical axis to the end on the upstream side in the main scanning direction is the third length, and the length from the optical axis to the end on the downstream side in the main scanning direction is the third length. a second constricted portion shaped to have a fourth length smaller than the length;
and a deflector that deflects the first light flux and the second light flux that have passed through the first aperture section and the second aperture section at positions shifted in the sub-scanning direction on the same plane. Device.
[2]
The optical scanning according to [1], wherein an aperture through which the first light flux passes through the first diaphragm and an aperture through which the second light flux passes through the second aperture are connected. Device.
[3]
The first aperture portion includes a first portion that shapes the shape of the first light flux to a first length from an optical axis to an upstream end in the main scanning direction; a second portion that shapes the shape of the light beam so that the length from the optical axis to the downstream end in the main scanning direction is a second length that is longer than the first length;
The second aperture portion includes a third portion that shapes the shape of the second light flux to a third length from the optical axis to the upstream end in the main scanning direction; and a fourth portion that shapes the shape of the light flux so that the length from the optical axis to the downstream end in the main scanning direction becomes a fourth length that is smaller than the third length.
the first portion and the fourth portion are formed in a first member;
The optical scanning device according to [1] or [2], wherein the second portion and the third portion are formed on a second member different from the first member.
[4]
The optical scanning device according to [1] or [2], wherein the first diaphragm portion and the second diaphragm portion are formed in one integrated member.
[5]
a first light source that emits a first light flux;
a second light source that emits a second light beam having an opening angle with respect to the first light beam in the main scanning direction and that exists upstream of the first light source in the main scanning direction;
The shape of the first light beam is defined so that the length from the optical axis to the end on the upstream side in the main scanning direction is the first length, and the length from the optical axis to the end on the downstream side in the main scanning direction is the first length. a first constriction shaped to have a second length greater than the length;
The shape of the second light beam is set so that the length from the optical axis to the end on the upstream side in the main scanning direction is the third length, and the length from the optical axis to the end on the downstream side in the main scanning direction is the third length. a second constricted portion shaped to have a fourth length smaller than the length;
a deflector that deflects the first light flux and the second light flux that have passed through the first aperture section and the second aperture section at positions shifted in the sub-scanning direction on the same plane;
and an image forming unit that transfers an electrostatic latent image formed by the first light flux and the second light flux deflected by the deflector onto a medium as an image.

100... Image forming apparatus 101... Printer 102... Scanner 115, 115C, 115K, 115M, 115Y... Image forming section 116... Optical scanning device 151, 151-7, 151-8... Polygon mirror 152 Motor 153 Light source 161, 162 Scanning optical system 170 Pre-deflection optical system 171 Collimator lens 172 Sub-scanning diaphragm 173 Cylinder lens 174, 174a, 174b, 174c, 174d, 200, 210, 300... main scanning diaphragm, 175a, 175b, 176a, 176b, 201, 202a, 202b, 221... aperture, 220... second main scanning diaphragm , 222...protrusion 230...fixing member 231...groove 1151...photoreceptor drum 1152...charging unit 1153...developing unit 1154...primary transfer roller 1155...cleaner, 1156... static elimination lamp, 1511... reflection surface, BY, BM, BC, BK, Ba, Bb, Bc, Bd... beam, OAM, OAY, OAa, OAb, OAc, OAd... optical axis

Claims (3)

a first light source that emits a first light flux;
a second light source that emits a second light beam having an opening angle with respect to the first light beam in the main scanning direction and that exists upstream of the first light source in the main scanning direction;
For the first light flux, the length from the optical axis to the upstream end in the main scanning direction is the first length, and the length from the optical axis to the downstream end in the main scanning direction is greater than the first length. a first diaphragm for shaping the shape of the first light beam so that it has a second length that is greater than the
The shape of the second light beam is set so that the length from the optical axis to the end on the upstream side in the main scanning direction is the third length, and the length from the optical axis to the end on the downstream side in the main scanning direction is the third length. a second constricted portion shaped to have a fourth length smaller than the length;
a deflector that deflects the first light beam and the second light beam that have passed through the first aperture unit and the second aperture unit at positions shifted in the sub-scanning direction on the same surface ,
The first aperture portion includes a first portion that shapes the shape of the first light flux to a first length from an optical axis to an upstream end in the main scanning direction; a second portion that shapes the shape of the light beam so that the length from the optical axis to the downstream end in the main scanning direction is a second length that is longer than the first length;
The second aperture portion includes a third portion that shapes the shape of the second light flux to a third length from the optical axis to the upstream end in the main scanning direction; and a fourth portion that shapes the shape of the light flux so that the length from the optical axis to the downstream end in the main scanning direction becomes a fourth length that is smaller than the third length.
the first portion and the fourth portion are formed in a first member;
The optical scanning device , wherein the second portion and the third portion are formed on a second member different from the first member . 2. The optical scanning according to claim 1, wherein an aperture through which said first light beam passes through said first diaphragm and an aperture through which said second light beam passes through said second diaphragm are connected. Device. a first light source that emits a first light flux;
a second light source that emits a second light beam having an opening angle with respect to the first light beam in the main scanning direction and that exists upstream of the first light source in the main scanning direction;
A rectangular first opening is provided, and the length from the optical axis of the first light beam incident on the first opening to the upstream end of the first opening in the main scanning direction is the first In the length 1, the length from the optical axis of the first light flux to the end of the first opening on the downstream side in the main scanning direction is set to a second length that is longer than the first length. a first diaphragm shaped into
A rectangular second opening is provided, and the length from the optical axis of the second light flux entering the second opening to the upstream end of the second opening in the main scanning direction is the second 3, the length from the optical axis of the second light flux to the downstream end of the second opening in the main scanning direction is set to a fourth length smaller than the third length. a second constriction shaped into
having a plurality of reflecting surfaces, and the first light flux on the upstream side in the main scanning direction and main scanning that have passed through the first diaphragm portion and the second diaphragm portion along the rotation direction of the plurality of reflecting surfaces; a deflector that deflects the second light beam on the downstream side of the direction at a position shifted in the sub-scanning direction on the same reflecting surface;
an image forming unit that transfers an electrostatic latent image formed by the first light flux and the second light flux deflected by the deflector onto a medium as an image ;
Both ends of the first rectangular opening in the main scanning direction are shifted in the main scanning direction from both ends of the second rectangular opening in the main scanning direction.
Image forming device.

Images